The two most important things that should be installed on a defensive carbine are a sling and a weapon light. The sling is like a holster for your rifle and the light is needed to positively identify threats in darkness or night. With how bright weapon lights are these days you can still illuminate a room with the carbine not pointed at the potential threat. With the rifle held in the high ready/port position or low ready position the light can still illuminate the room enough to identify any potential threats without having to point your weapon and weapon light at anyone before they are identified as a threat.
A few years back a company called Cloud defensive released the optimized weapon light (owl). It is very bright and the light carries very far with 1,250 lumens and 50,000 candela. Spill is how much of an area that the light covers. The higher the candela, the smaller the spill. Spill is great for defensive lights because lights with more spill or less candela cover a bigger field of view because the beam is less concentrated. Even though this light has very high candela, I find it to have enough spill to illuminate rooms for indoor and small structure use as well as being able to have a concentrated enough beam to identify objects out to 200 yards.
My first impression of this light is big and heavy. These are the only downsides to it that I have found so far. Although, the tradeoffs for having the big and heavy light are that it is very durable, a very high performer, and less likely to malfunction with no exposed wires. Pressure pad is very nice, has momentary and constant function. If you hold the pad, the light will shut off as soon as you let off the switch. If you click the switch on it will stay on and when you would like to turn it off just click it again. The bezel and rear cap can be reversed without having to buy extra parts so it is left hand and right hand shooter friendly. It is even shaped well enough that the pressure pad can be accessed even when shooting support side. The pressure pad is very intuitive as long as you don’t mind using a c clamp grip that is required to operate the switch. I like that there are no exposed wires to worry about catching on stuff or having to worry about kinking the wires and getting shorts. The light seems expensive, starting around $370 but ships with both a charger and two rechargeable batteries which is a great deal. With one backup battery, there is always one that can be rotated into the light when one dies. The extra battery can either be stored in the pistol grip or stock on the carbine. This light can only be run on 18650 batteries and the manufacture will not warranty it if you run cr123 batteries in it.
In low light with iron sights, I am able to positively id a human sized target at 100 yards. Also In low light with a low power variable scope I am able to pid a human sized target at 200 yards.
Happy Shooting and Have a Great Weekend!